feat(ECR-041): OpsCMS Banner 薄写面（Write-Wave 首刀）

Admin POST/PUT + admin.cms.write/审计；C 端 GET /home/banners；首页投影回退静态 homeFeeds；migration 000051；不碰 FeedSlot/支付/UGC。

Co-authored-by: Cursor <cursoragent@cursor.com>

proto/openapi.yaml

@@ -778,6 +778,21 @@ paths:
           description: Unauthorized
         '403':
           description: Forbidden
+    post:
+      tags: [admin]
+      summary: Create Banner
+      description: Requires admin.cms.write · ECR-041
+      responses:
+        '200':
+          description: OK
+        '400':
+          description: Invalid
+        '401':
+          description: Unauthorized
+        '403':
+          description: Forbidden
+        '409':
+          description: Code conflict
 
   /api/v1/admin/cms/banners/{id}:
     get:
@@ -793,6 +808,26 @@ paths:
           description: OK
         '404':
           description: Not found
+    put:
+      tags: [admin]
+      summary: Update Banner
+      description: Requires admin.cms.write · deactivate via active=false
+      parameters:
+        - in: path
+          name: id
+          required: true
+          schema: { type: string, format: uuid }
+      responses:
+        '200':
+          description: OK
+        '400':
+          description: Invalid
+        '403':
+          description: Forbidden
+        '404':
+          description: Not found
+        '409':
+          description: Code conflict
 
   /api/v1/admin/cms/feed-slots:
     get:
@@ -1448,6 +1483,18 @@ paths:
         '200':
           description: OK
 
+  /api/v1/home/banners:
+    get:
+      tags: [system]
+      summary: Homepage active banners (ECR-041)
+      parameters:
+        - in: query
+          name: placement
+          schema: { type: string, default: home, enum: [home, explore, ask] }
+      responses:
+        '200':
+          description: OK
+
   /api/v1/home/daily-tips:
     get:
       tags: [system]